1. Field of the Invention
The present invention relates to a conductive elastomer composition, a method of producing it, and conductive members composed of the conductive elastomer composition. More particularly, the conductive elastomer composition is used suitably for conductive members such as conductive belts including a transfer belt and conductive rollers including a transfer roller, a driving roller, a developing roller, and a charging roller for a copying machine, a printer, and the like. The present invention is intended to allow the conductive elastomer composition to have rubber-like durability, elasticity, and flexibility, resin-like moldability, and a low electric resistance by improving an ionic-conductive agent to be contained in the conductive elastomer composition.
2. Description of the Related Art
It is necessary that conductive members such as conductive belts including a transfer belt and conductive rollers including a transfer roller, a driving roller, a developing roller, and a charging roller for a copying machine, a printer, and the like have an appropriate stable electric resistance value.
As a method of imparting electric conductivity to the conductive member of this kind, the following two methods are known: In one of them, an electroconductive polymer composition containing a conductive filler such as powder of metal oxide or carbon black is used; and in the other method, an ionic-conductive polymer such as urethane rubber, acrylonitrile-butadiene rubber (NBR), and epichlorohidrin rubber is used.
In the case where the electroconductive polymer composition is used, there is a region in which an electric resistance changes rapidly owing to a slight change of an addition amount of a conductive filler. Thus it is very difficult to control the electric resistance. In addition, because it is difficult to disperse the conductive filler uniformly in the polymer composition, an electric resistance value has variations in the circumferential and widthwise directions of the conductive roller. Further because the electric resistance value of the conductive roller depends on an applied voltage, the conductive roller does not have a constant electric resistance value.
Thus as the recent tendency, a conductive member composed of the ionic-conductive polymer is used rather than a roller composed of the electroconductive polymer in a copying machine and a printer required to form a high-image quality by using digital image processing technique and color image processing technique and save energy. Various ionic-conductive polymers have been proposed.
For example, in Japanese Patent Application Laid-Open No.8-34929, to enhance ionic conductivity and mechanical strength of the ionic-conductive polymer, there is disclosed the polymeric solid electrolyte. The low-polarity polymeric phase of the polymeric solid electrolyte has a crosslinking structure. The polymeric component of the low-polarity polymeric phase has double bonds. A part of the double bonds cleaves to form an intramolecular or intermolecular crosslinking.
In Japanese Patent Application Laid-Open No.8-183866, there is disclosed a sheet composed of the thermoplastic elastomer containing the olefin thermoplastic elastomer used as its main component and the permanent antistatic agent and a method of producing the sheet composed of the thermoplastic elastomer. The sheet is developed to be recycled and to prevent electrical troubles from occurring.
However, the polymeric solid electrolyte disclosed in Japanese Patent Application Laid-Open No.8-34929 has problems that the material cost and the producing cost are high, and both a low compression strain and thermoplasticity cannot be realized.
In the sheet disclosed in Japanese Patent Application Laid-Open No.8-183866, the permanent antistatic agent is contained in the olefin thermoplastic elastomer not to reduce the volume resistivity of the sheet but to lower the surface resistance value to thereby realize antistatic performance. Thus the sheet has a high electric resistance. On the basis of the fundamental components (ultraviolet ray-absorbing agent, HALS, and colorant not affecting compression set and conductivity are not used) of the example 3 shown in table 1, a conductive specimen of the comparison example 4 shown in table 2 has been formed as an experiment. The result was that the specimen had a large compression set and did not have a preferable property value. An antistatic agent containing an electrically conductive plasticizer is conceivable. However, such an antistatic agent damages mechanical property of the sheet composed of the thermoplastic elastomer, deteriorates the compression set thereof, and stains a photosensitive member. Thus the sheet disclosed in Japanese Patent Application Laid-Open No.8-183866 cannot be used for the conductive member for a copying machine and the like.
The ionic-conductive polymer practically used for the conductive member is composed mainly of a vulcanized rubber composition which cannot be recycled. It is conceivable to use not the vulcanized rubber composition but a chlorine-containing thermoplastic elastomer. However, the chlorine-containing thermoplastic elastomer has a large compression set and stains the photosensitive member. Further there is a fear that the chlorine-containing thermoplastic elastomer generates a harmful gas such as hydrogen chloride and dioxine when it burns. People are now very conscious of environmental problems. Thus the chlorine-containing thermoplastic elastomer has a problem in handling it when it is discarded.